更新dtd格式

liteflow-core/src/main/resources/dtd/liteflow.dtd

@@ -9,7 +9,7 @@
         id CDATA #REQUIRED
         type (script|if_script|switch_script|while_script|for_script|break_script) #IMPLIED
         class CDATA #IMPLIED
-        language (groovy|js) #IMPLIED
+        language (groovy|js|python) #IMPLIED
         >
 <!ATTLIST chain
         name CDATA>